What is the origin of "Shave and a Haircut"?

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Why: In Who Framed Roger Rabbit?, no toon can resist finishing it - "two bits." Except when I was little, we said:

Shave and a haircut - shampoo
You said a mouthful - shut up

Answer: The name actually refers to the musical couplet that's the tune when you're singing it. The first known occurrence of the tune is from an 1899 Charles Hale song, "At a Darktown Cakewalk." The same notes form the bridge in the still-popular "Hot Scotch Rag", written by H.A. Fischler in 1911.

In 1939, Dan Shapiro, Lestor Lee and Milton Berle released "Shave and a Haircut—Shampoo," which featured the tune in the closing bars. This is thought to be the origin of the lyrics.

Source: Wikipedia

The More You Know: "Two bits" is a colloquial U.S. expression for 25 cents (like in Once Upon a Time in America: "He's altogether lovable / But he'll always be a two-bit punk / So he'll never be my beloved /What a shame"). Other variations:

• "Six bits" - in the book Rascal by Sterling North
• "Get lost"
• "Five bob" - in the UK